A transponder, as used herein, refers to any number of devices that are configured to receive a charge from an external device and to transmit a wireless signal in response. For example, one type of transponder is an RFID tag that is powered by a wand (or reader) that emits radiation, wherein the RFID tag uses power in the radiation in order to transmit a signal that may be read by the wand. Other transponders may be powered by other energy sources to similarly provide enough power to the transponder to transmit a signal that is readable by a wand (or other reading device). Another example transponder, referred to as an embedded passive integrated transponder, is discussed in co-pending application Ser. No. 12/371,048, filed Feb. 13, 2009, entitled “Method and apparatus for locating passive integrated transponder tags,” which is hereby incorporated by reference in its entirety and for all purposes.